Determination and transdetermination in imaginal discs of Drosophila must be underlain by some form of control system having sharply alternate self maintained states. If many such subsystems or circuits are involved, the combinations of their states may be characterized as an epigenetic code. Recently, I suggested determination is due to at least 4 circuits each with two alternate states. Thus leg Triple bond 1010, wing Triple bond 1111, where 1 is the more stable state of each circuit. To test this model, I hope to achieve somatic cell fusion of disc cells, then test the determined state of the fused cell. If the more stable "1" state dominates, leg x wing equals 1010 x 1111 yields 1111 or wing, while haltere fused with antenna (0111 x 1100 yields 1111) should yield wing. I have three complementing temperature sensitive cell lethal Drosophila mutants. Each carries a recessive visible cuticle marker. I am disaggregating and coreaggregating 3rd instar imaginal discs of two T. S. strains, treating with various chemical and viral agents to induce fusion, implanting the aggregate in 3rd instar larvae to induce the metamorphosis of the reaggregate with the heat, and hoping to select for wild type fused cells at the nonpermissive temperature. In addition, I am searching among homeotic mutants, to find those which switch a determination circuit from one to another state. This requires use of somatic recombination to mark clones, and experiments to distinguish whether homeotic conversion, say of antenna to leg, is due to an alteration in determintion itself, or other processes.